Ceramic powder and multi-layer ceramic capacitor

ABSTRACT

A multi-layer ceramic capacitor is made by alternately layering a dielectric layer constituted by a sintered body of a ceramic powder, and an internal electrode layer. The ceramic powder contains barium titanate powder having a perovskite structure with a median size of 200 nm or smaller as measured by SEM observation, wherein the barium titanate powder is such that the percentage of barium titanate particles having twin defects in the barium titanate powder is 13% or more as measured by TEM observation and that its crystal lattice c/a is 1.0080 or more. The ceramic powder has a wide range of optimum sintering temperatures and thus offers excellent productivity and is particularly useful in the formation of thin dielectric layers of 1 μm or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No. 13/849,367, filed Mar. 22, 2013, which claims priority to Japanese Patent Application No. 2012-080787, filed Mar. 30, 2012, each disclosure of which is herein incorporated by reference in its entirety. The applicant herein explicitly rescinds and retracts any prior disclaimers or disavowals made in any parent, child or related prosecution history with regard to any subject matter supported by the present application.

BACKGROUND

1. Field of the Invention

The present invention relates to a ceramic powder that contains barium titanate having a perovskite structure, and a multi-layer ceramic capacitor (MLCC) obtained by using said ceramic powder, particularly useful for a MLCC using a thin-layer dielectric layer.

2. Description of the Related Art

Multi-layer ceramic capacitors (MLCCs) are used in various electronic devices including mobile devices and communications devices.

The trend for smaller, higher-performance MLCCs and other electronic components has been prominent in recent years and, in the case of MLCCs, for example, these capacitors are becoming significantly smaller and larger in capacity. The capacity of a MLCC is proportional to the number of dielectric layers constituting the base material of the MLCC, and inversely proportional to the thickness per dielectric layer, and consequently it is desirable to keep the dielectric layer thin, such as 1 μm or less, and increase the number of layers.

For the material ceramic powder with which to form such dielectric layer, barium titanate powder having a perovskite structure is widely used.

To ensure performance and reliability, and also from the viewpoint of physical characteristics, it is important that the barium titanate powder consist of fine particles so as to make the aforementioned dielectric layer thinner.

Here, one proposed method to synthesize a barium titanate compound suitable for making the dielectric layer thinner is to crush and mix with an organic solvent a powder mixture containing barium carbonate powder and titanium dioxide powder, and then sinter the crushed and mixed powder mixture to obtain a powder of barium titanate compound (Patent Literature 1).

According to Patent Literature 1, the powder of barium titanate compound obtained by the method described therein has an average particle size of 100 nm or smaller, contains twin defects in at least 10% of the particles, and its standard deviation of particle distribution is 20 or smaller. It is also described that, by using this powder, variation of surface roughness can be suppressed and consequently the shorting rate and insulation resistance failure of the MLCC can be suppressed.

BACKGROUND ART LITERATURE Patent Literature

-   [Patent Literature 1] Japanese Patent Laid-open No. 2011-132071

SUMMARY

However, while Patent Literature 1 does not present specific data on electrical characteristics, such barium titanate ceramic powder with a small particle size of 100 nm or smaller is generally subject to a significant variation in the electrical characteristics of the obtained dielectric layer, relative to changes in the oxygen partial pressure, temperature, and other sintering conditions, for example, when the powder is sintered and made into the dielectric layer. In other words, the range of optimum sintering temperatures is narrow.

Generally when manufacturing a MLCC, laminates called “green sheets,” each constituted by internal electrode layers and layers containing ceramic powder, are stacked and layered on top of one another to create many MLCC moldings, which are then placed into a sintering furnace and sintered all at once.

For this reason, it is difficult to heat each molding in a completely uniform manner, and because sintering irregularities occur whereby sintering is promoted more in some parts and suppressed in other parts, a narrow range of optimum sintering temperatures leads to defects and consequently a lower yield.

Accordingly, the method described in Patent Literature 1 is not expected to produce a high yield, because changes in the sintering conditions, even minor changes in the temperature or oxygen partial pressure, will significantly affect the characteristics of the resulting MLCC and also reduce the yield considerably.

Accordingly, an object of the present invention is to provide a ceramic powder whose main ingredient is barium titanate having a perovskite structure, wherein said powder has a wide range of optimum sintering temperatures and thus offers excellent productivity and is particularly useful in the formation of thin dielectric layers of 1 μm or less, so that highly reliable, uniform MLCC products can be provided at a high yield.

The inventor of the present invention completed the present invention after discovering that such problems could be resolved by a ceramic powder which has a specific average particle size or smaller, exhibits twin defects by a specific percentage or more, and contains barium titanate of high tetragonality whose crystal lattice c/a is at or higher than a specific value.

In other words, the present invention is a ceramic powder that contains barium titanate having a perovskite structure, with an average particle size (median size) of 200 nm or smaller as measured by SEM observation, wherein said ceramic powder is such that the percentage of twin defects in the barium titanate is 13% or more as measured by TEM observation and that its crystal lattice c/a is 1.0080 or more.

To obtain an excellent dielectric layer, it is desirable that the aforementioned barium titanate has an average particle size of 80 to 200 nm.

Preferably the barium titanate having a perovskite structure to constitute the ceramic powder proposed by the present invention has a percentage of twin defects of 13 to 23% and a lattice c/a of 1.0091 to 1.0105. By using the ceramic powder proposed by the present invention, which meets the above ranges, MLCCs can be produced at a high yield.

Furthermore, the MLCC proposed by the present invention is made by alternately layering a dielectric layer constituted by a sintered body of the ceramic powder proposed by the present invention, and an internal electrode layer.

According to the present invention, a ceramic powder is provided whose main ingredient is barium titanate having a perovskite structure, wherein said powder has a wide range of optimum sintering temperatures and thus offers excellent productivity and is useful in the formation of thin dielectric layers of 1 μm or smaller, and by using this ceramic powder, MLCCs can be manufactured at a high yield and consequently the MLCC manufacturing cost can be reduced.

Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.

For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

Further aspects, features and advantages of this invention will become apparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention. The drawings are greatly simplified for illustrative purposes and are not necessarily to scale.

FIG. 1 is a simple drawing showing a barium titanate particle in which twin defects are formed.

FIG. 2 is a schematic longitudinal cross-section view of a multi-layer ceramic capacitor conforming to the present invention.

DESCRIPTION OF THE SYMBOLS

-   -   1 Multi-layer ceramic capacitor     -   10 Ceramic sintered body     -   11 Laminate     -   12 Dielectric layer     -   13 Internal electrode layer     -   15 Cover layer     -   20 External electrode

DETAILED DESCRIPTION OF EMBODIMENTS

As mentioned above, the ceramic powder proposed by the present invention contains barium titanate having a perovskite structure, and the average particle size (median size) of the barium titanate as measured by observation using a scanning electron microscope (SEM) is 200 nm or smaller. The particle size can be the maximum width of the particle observed with SEM. The median size is the particle size of the median particle (d50) when counting particles in the order of the size.

The aforementioned average particle size can be obtained by observing a powder sample of barium titanate using a SEM wherein n=500 (measuring 500 particles), and then taking the median size of the measured particles. The 500 particles can be selected randomly or can be all the particles observed in a randomly selected region or regions.

If the average particle size is 200 nm or larger, a smooth and highly reliable dielectric layer of 1 μm or less in thickness cannot be obtained.

Additionally, the average particle size is normally 80 nm or more, or preferably 80 to 200 nm from the viewpoint of obtaining a thin dielectric layer from the ceramic powder proposed by the present invention. How to adjust the average particle size will be described later.

Next, the aforementioned barium titanate having a perovskite structure has a percentage of twin defects, as measured by observation using a transmission electron microscope (TEM), of 13% or more. The percentage of twin defects is measured by observing a powder of the barium titanate using a TEM and counting, among 100 particles (n=100 wherein the 100 particles can be selected randomly or can be all the particles observed in a randomly selected region or regions), those particles in which twin defects are formed. FIG. 1 shows a schematic drawing of a barium titanate particle in which twin defects are formed (the right particle with two lines).

Under the present invention, probably the fact that the percentage of twin defects in the barium titanate having a perovskite structure is 13% or more and that its crystal lattice c/a is at a specific value or more produces some kind of synergistic effect and gives a wide range of optimum sintering temperatures to the ceramic powder of the present invention.

From such viewpoint, preferably the aforementioned percentage of twin defects is 13 to 23%. How to adjust the percentage of twin defects will be described later.

As mentioned above, the crystal lattice c/a of the barium titanate having a perovskite structure is 1.0080 or more. The c/a can be obtained by measuring the diffraction peak of the barium titanate (as a barium titanate powder sample in its entirety) according to any known powder X-ray diffraction method, analyzing the obtained diffraction peak according to the Rietveld method, and then calculating the lattice constants for axis a and axis c.

Such ceramic powder proposed by the present invention, having high tetragonality of barium titanate and a certain percentage or more of twin defects, has a wide range of optimum sintering temperatures and this wide sintering temperature range can be used to manufacture MLCCs at a high yield. In this disclosure, the “ceramic powder” contains the “barium titanate powder” as a main or predominant composition, consists essentially of the “barium titanate powder”, is characterized by the “barium titanate powder”, or is equivalent to the “barium titanate powder”.

In addition, high tetragonality of barium titanate is desirable because the dielectric constant of barium titanate will increase and the MLCC will have a higher capacity.

From the above viewpoints, preferably the c/a is 1.0091 to 1.0105 because, as long as this c/a range is maintained, any capacity variation of the MLCC obtained using the ceramic powder of the present invention will remain 2% or less. How to adjust the c/a will be described later.

Next, how to manufacture the ceramic powder proposed by the present invention is explained. The manufacturing method is not limited in any way, so long as the barium titanate constituting the main ingredient of the powder meets the various parameters explained above. However, the powder can be manufactured as described below by considering and adjusting the various conditions and factors, for example.

In general, titanium material and barium material are reacted with each other to synthesize barium titanate, which is then heat-treated and sintered into a ceramic powder, after which the powder is crushed to adjust the particle size as necessary and, if necessary, the crushed powder is further mixed with various additive compounds.

Various methods have been known to synthesize the aforementioned barium titanate, where examples include the sol-gel method, hydrothermal method, and solid phase method.

Among these methods, the sol-gel method and hydrothermal method tend to suppress generation of twin defects and lower the c/a value.

The solid phase method tends to generate more twin defects and raise the c/a value.

In addition, the c/a value tends to rise if the ratio of barium and titanium (Ba/Ti) in the synthesized barium titanate is slightly greater than the stoichiometric level, or it tends to drop if this ratio is lower than the stoichiometric level. This ratio does not affect the percentage of twin defects much.

Furthermore, under the present invention, preferably the aforementioned heat treatment is implemented in two separate stages of hydrothermal treatment and heat treatment.

If the temperature or time of the aforementioned heat treatment is higher or longer, the percentage of twin defect generation increases and the c/a value tends to rise. Conversely if the temperature or time of heat treatment is lower or shorter, generation of twin defects is suppressed and the c/a value tends to drop.

The aforementioned hydrothermal treatment is realized by introducing into water or specified aqueous solution or other liquid the barium titanate powder that has been synthesized by the sol-gel method, etc., and then adding thermal energy to the powder using the liquid as the medium.

Preferably the hydrothermal treatment temperature is 100° C. or higher, because the tetragonality of barium titanate is not expected to increase much when this temperature is lower than 100° C. The hydrothermal treatment temperature is normally 200° C. or lower.

The hydrothermal treatment time is not limited in any way, but at least one hour of hydrothermal treatment is enough and normally the treatment time is 12 hours or less. As for the pressure of hydrothermal treatment, sufficient effects can be expected at a pressure of at least 1 MPa.

In addition, while the liquid for hydrothermal treatment may be water, it is preferable to use an aqueous solution that contains A-site metal ions of the aforementioned barium titanate having a perovskite structure, or specifically barium ions, to a certain concentration, or desirable to use an aqueous solution that contains A-site metal ions by at least 0.1 times the mole number of A-site metal contained in the powder to be treated.

After the hydrothermal treatment, the barium titanate powder is dried and then heat-treated to increase the particle size and thereby obtain a barium titanate powder having a desired average particle size. This heat treatment further increases the percentage of twin defects in barium titanate and the c/a value of its crystal lattice.

Conditions of the aforementioned heat treatment are not limited in any way, but the heat treatment, normally, is performed under the conditions of 500 to 1200° C. for 0.5 to 6 hours, or preferably under the conditions of 890 to 970° C. for 2 to 6 hours. This heat treatment may be performed in atmosphere or in an ambience of N₂, etc.

By providing heat treatment at a specific temperature for a specified time as mentioned above, the level of particle growth can be controlled and a desired average particle size can be achieved. While the average particle size of barium titanate powder is normally 10 to 40 nm before sintering, this heat treatment (sintering) increases the size normally to as much as 80 to 200 nm.

The heat treatment explained above increases the percentage of twin defects in barium titanate and raises the c/a value of crystal lattice.

The barium titanate powder thus obtained is crushed to adjust the particle size, as necessary, or crushing is combined with classification to regulate the particle size.

This crushing can be done using either a wet method or dry method, but dry crushing is preferred from the viewpoint of drying cohesion. Note, however, that dry crushing tends to lower the c/a value. It does not affect the percentage of twin defects much.

Under the present invention, individual conditions, etc., are adjusted/set as deemed appropriate, with an understanding of what each of the above operations tends to do, to manufacture a barium titanate powder having a perovskite structure and meeting the average particle size, percentage of twin defects and c/a value as specified under the present invention.

Particularly under the present invention, it is preferable to obtain a barium titanate powder by: manufacturing barium titanate according to the sol-gel method or solid phase method; hydrothermally treating the manufactured barium titanate under the conditions of 110 to 120° C. for 2 to 24 hours at a pH of 13.0 to 13.5; heat-treating the hydrothermally treated barium titanate under the conditions of 890 to 970° C. for 2 to 6 hours; and dry-crushing the heat-treated barium titanate as necessary.

The ceramic powder proposed by the present invention contains a barium titanate powder obtained in the manner described above, for example, and it also contains various additive compounds as necessary, as described later.

For example, the ceramic powder proposed by the present invention, being obtained as explained above, has a wide range of optimum sintering temperatures and a small average particle size, and these characteristics can be used to manufacture, at a high yield, high-quality MLCCs having a dielectric layer of 1 μm or less in thickness. Manufactured MLCCs have sufficient capacitance, present less capacitance variation among individual products, and are resistant to defects.

Next, a multi-layer ceramic capacitor according to an embodiment of the present invention is explained. FIG. 2 is a schematic longitudinal cross-section view of a multi-layer ceramic capacitor 1 conforming to the present invention.

The multi-layer ceramic capacitor 1 is generally constituted by a ceramic sintered body 10 having standard chip dimensions and shape (such as a rectangular solid of 1.0×0.5×0.5 mm), and a pair of external electrodes 20 formed on both sides of the ceramic sintered body 10. The ceramic sintered body 10, whose main ingredient is barium titanate particle crystal, has a laminate 11 formed by alternately layering dielectric layers 12 and internal electrode layers 13 inside, and cover layers 15 formed as the outermost layers provided at the top and bottom in the laminating direction.

The laminate 11, where each dielectric layer 12 sandwiched by two internal electrode layers 13 has a thickness of 1 μm or less (such as approx. 900 nm) according to the specifications of capacitance and required pressure resistance, etc., has a high-density, multi-layer structure comprising several dozen to several hundred layers in total.

The cover layers 15 formed as the outermost layers of the laminate 11 protect the dielectric layers 12 and internal electrode layers 13 from external contamination due to humidity, contaminants, etc., and prevent deterioration of these layers over time.

The multi-layer ceramic capacitor 1 is manufactured as follows, for example. First, a material fine-particle powder whose main ingredient is barium titanate is wet-mixed with additive compounds, after which the mixture is dried and crushed to prepare a dielectric powder (ceramic powder conforming to the present invention). Examples of the additive compounds include oxides of Mg, Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Cr, V, Mn, Co, Ni, Nb, Ta, Mo, W, Si, Li, B, Na and K, among others. These additive compounds, normally, are added by 0.01 to 0.1 mol in total, per 1 mol of barium titanate.

The prepared dielectric powder is wet-mixed using a binder such as polyvinyl butyral resin, and an organic solvent such as ethanol, after which the mixture is coated on a base material in a band form as a dielectric green sheet of 1 μm or less in thickness according to the die-coater method, doctor blade method, etc., and then dried. Next, a metal conductive paste containing organic binder is printed on the surface of the dielectric green sheet by means of screen printing or gravure printing, to place an internal electrode layer 13 pattern. For the aforementioned metal, nickel is widely used from the viewpoint of cost.

It is possible to uniformly disperse barium titanate with an average particle size of 50 nm or smaller, in the aforementioned metal conductive paste, as a co-material. Thereafter, a specified number of dielectric green sheets, which have been stamped out to an identical size of 15 cm×15 cm, for example, are layered so that the internal electrode layers 13 and dielectric layers 12 alternate. Cover sheets that will become cover layers 15 are then pressure-bonded at the top and bottom of the layered dielectric green sheets, after which the laminate is cut to specified chip dimensions (such as 1.0 mm×0.5 mm) and then a Ni conductive paste that will form external electrodes 20 is coated on both side faces of the laminate and dried. This way, a molding of multi-layer ceramic capacitor 1 is obtained.

The molding of multi-layer ceramic capacitor 1 thus obtained is placed in a N₂ ambience of approx. 350° C. to remove the binder, and then sintered for 10 minutes to 2 hours at 1100 to 1280° C. under a mixed gas containing N₂, H₂ and H₂O (whose oxygen partial pressure is approx. 1.0×10⁻¹¹ MPa), to obtain a multi-layer ceramic capacitor 1.

In the obtained multi-layer ceramic capacitor 1, the internal electrode layers 13 are embedded in such a way that their edges are exposed alternately at both end faces of the dielectric layers 12 in the length direction, where the exposed edges of internal electrode layers 13 are connected to the external electrodes 20.

Also, the thickness of the dielectric layer 12 is normally 3 μm or less, or preferably 0.5 to 1 μm, while the thickness of the internal electrode layer 13 is normally 0.5 to 3 μm. With the ceramic powder proposed by the present invention, the average particle size of its main ingredient, or specifically barium titanate, is controlled to 200 nm or smaller, and therefore a surface of excellent smoothness can be achieved even on such thin dielectric layer and, consequently a multi-layer ceramic capacitor resistant to shorting and other problems can be obtained.

Furthermore, the aforementioned sintering forms particles of the core-shell structure, where each particle has a core of barium titanate being the main ingredient of the aforementioned dielectric powder, and a shell constituted by the aforementioned additive compounds and solid solution of barium titanate, and this structure adds favorable temperature characteristics to the dielectric layer and keeps changes in capacitance and other performance-related characteristics to a minimum, even when the MLCC is subject to changing ambient temperatures.

EXAMPLES Example 1

A barium titanate powder having a perovskite structure was obtained according to the method described below.

First, a barium titanate powder of 15 nm in average particle size and 1.0021 in Ba/Ti ratio, synthesized by the sol-gel method, was hydrothermally treated under the conditions of 120° C. for 6 hours at a pH of 13.5, and then heat-treated (sintered) in a N₂ ambience of 970° C. for 2 hours, to obtain a barium titanate powder having a perovskite structure. The average particle size of the barium titanate was 145 nm, percentage of particles containing twin defects was 16%, and c/a was 1.0101.

As for the average particle size, a powder sample was observed using a SEM and sizes of 500 particles were measured, and the median size (diameter) was taken as the average particle size.

The percentage of twin defects was obtained by observing a powder sample using a TEM and counting, among 100 particles, those particles in which twin defects were formed.

Furthermore, the c/a was obtained by X-ray diffraction measurement of powder, followed by the Rietveld analysis.

The obtained barium titanate powder was used as the material to obtain a ceramic powder based on a X7R dielectric composition {(100 BaTiO₃-1.0 HO₂O₃-1.0 MgO-0.7 MnO₂-1.5 SiO₂); the unit is mol}, after which a MLCC molding was prepared using a normal method and then sintered in a sintering furnace, to prepare a MLCC having 50 dielectric layers, 51 nickel internal electrode layers, and thickness per dielectric layer of 1 μm.

When one hundred MLCC samples were measured for capacitance to evaluate the average capacitance and a standard deviation relative to the average capacitance, the following results were obtained, suggesting that the obtained MLCCs presented a very uniform capacitance distribution.

Cap=1.08 μF.σ/ X =1.7%  [Mathematical Formula 1]

As for the aforementioned standard deviation (variation in capacitance), samples with a standard deviation of less than 3.0% were judged acceptable because the greater the variation, the lower the yield on capacitance becomes.

Since the samples presented a small variation in capacitance as is evident above, the ceramic powder proposed by the present invention provides a wide range of optimum sintering temperatures and achieves high productivity.

The above results are summarized in Tables 1 and 2 below. It should be noted that a TEM analysis of sintered MLCCs found that the measured MLCCs contained twin defects at a percentage equivalent to the percentage of twin defects in the material barium titanate powder used in the manufacture thereof.

Comparative Example 1

When the barium titanate powder having a perovskite structure as obtained in Example 1 was passed through an air jet type dry crusher (Jetmizer) twice, the average particle size of the aforementioned powder became 130 nm, while the c/a became 1.0078. The percentage of particles containing twin defects remained unchanged at 16% as before the crushing.

This barium titanate powder was used as the material to obtain a ceramic powder of the same composition as in Example 1, to create a MLCC having 50 dielectric layers, 51 nickel internal electrode layers, and thickness per dielectric layer of 1 μm. When 100 MLCC samples were evaluated for capacitance and a standard deviation relative to the average capacitance, the following results were obtained, suggesting that the obtained MLCCs had a poor capacitance distribution and large variation in capacitance.

Cap=0.98 μF.σ/ X =3.2%  [Mathematical Formula 2]

The above results are summarized in Tables 1 and 2 below. It should be noted that a TEM analysis of sintered MLCCs found that the measured MLCCs contained twin defects at a percentage equivalent to the percentage of twin defects in the material ceramic powder used in the manufacture thereof.

Examples 2 to 13, Comparative Examples 2 to 4

Barium titanate powders were manufactured in the same manner as in Example 1, except that the method for synthesizing barium titanate, average particle size before/after heat treatment, Ba/Ti ratio, various heat treatment conditions, crushing conditions, generation ratio of twin defects, and c/a value, were changed as shown in Table 1 below.

The obtained barium titanate powder was used as the material to prepare a ceramic powder of the same composition as in Example 1, after which a MLCC molding was created according to a normal method and then sintered in a sintering furnace, to prepare a MLCC having 51 nickel internal electrode layers and a thickness of 1 μm per dielectric layer. One hundred MLCC samples were measured to evaluate the capacitance and a standard deviation relative to the average capacitance.

The results are shown in Table 2 below. It should be noted that, in all examples, a TEM analysis of sintered MLCCs found that the measured MLCCs contained twin defects at a percentage equivalent to the percentage of twin defects in the material ceramic powder used in the manufacture thereof.

TABLE 1 BaTiO₃ material Average Percentage Average Treatment [1] Treatment [2] particle of twin particle Method of Hydrothermal Heat Dry size defects size synthesis Ba/Ti treatment treatment crushing nm % c/a Example [1] 15 nm Sol-gel 1.0021 120° C./ 970° C./ None 145 16% 1.0101 method 6 hours/ 2 hours/ pH of 13.5 N₂ ambience Example [2] 15 nm Sol-gel 1.0021 120° C./ 970° C./ 1-pass 135 16% 1.0091 method 6 hours/ 2 hours/ pH of 13.5 N₂ ambience Comparative 15 nm Sol-gel 1.0021 120° C./ 970° C./ 2-pass 130 16% 1.0078 Example [1] method 6 hours/ 2 hours/ pH of 13.5 N₂ ambience Example [3] 37 nm Sol-gel 0.9993 120° C./ 930° C./ None 195 23% 1.0104 method 12 hours/ 2 hours/ pH of 13 N₂ ambience Example [4] 37 nm Sol-gel 0.9993 120° C./ 930° C./ 1-pass 190 23% 1.0096 method 12 hours/ 2 hours/ pH of 13 N₂ ambience Example [5] 37 nm Sol-gel 0.9993 120° C./ 930° C./ 2-pass 185 23% 1.0085 method 12 hours/ 2 hours/ pH of 13 N₂ ambience Comparative 20 nm Hydrothermal 1.0015 120° C./ 945° C./ None 85 11% 1.0093 Example [2] method 24 hours/ 2 hours/ pH of 13.5 N₂ ambience Comparative 20 nm Hydrothermal 1.0015 120° C./ 945° C./ 1-pass 80 11% 1.0083 Example [3] method 24 hours/ 2 hours/ pH of 13.5 N₂ ambience Example [6] 25 nm Solid phase 0.9995 120° C./ 960° C./ None 150 19% 1.0101 method 16 hours/ 2 hours/ pH of 13 atmosphere Example [7] 25 nm Solid phase 0.9995 120° C./ 960° C./ 1-pass 145 19% 1.0093 method 16 hours/ 2 hours/ pH of 13 atmosphere Example [8] 25 nm Solid phase 0.9995 120° C./ 960° C./ 2-pass 140 19% 1.0083 method 16 hours/ 2 hours/ pH of 13 atmosphere Example [9] 10 nm Sol-gel 1.0026 120° C./ 890° C./ None 135 13% 1.0092 method 8 hours/ 6 hours/ pH of 13.5 atmosphere Example [10] 10 nm Sol-gel 1.0026 120° C./ 890° C./ 1-pass 130 13% 1.0080 method 8 hours/ 6 hours/ pH of 13.5 atmosphere Comparative 25 nm Hydrothermal 0.9996 120° C./ 890° C./ None 105 11% 1.0077 Example [4] method 24 hours/ 3 hours/ pH of 13.5 atmosphere Example [11] 10 nm Sol-gel 1.0015 110° C./ 900° C./ None 80 13% 1.0090 method 2 hours/ 2 hours/ pH of 13.5 N₂ ambience Example [12] 10 nm Sol-gel 1.0015 110° C./ 900° C./ None 90 13% 1.0092 method 2 hours/ 2.5 hours/ pH of 13.5 N₂ ambience Example [13] 10 nm Sol-gel 1.0015 110° C./ 900° C./ None 95 14% 1.0095 method 2 hours/ 4 hours/ pH of 13.5 N₂ ambience

For example, a comparison of Examples 1 and 2 and Comparative Example 1 shows that dry crushing reduces the average particle size of barium titanate powder and also reduces the c/a, without affecting the percentage of twin defects, while a comparison of Examples 11 to 13 finds that a longer heat treatment increases the average particle size and causes both the percentage of twin defects and c/a to become higher.

Additionally, Comparative Example 4 shows that neither the required percentage of twin defects nor c/a can be achieved, depending on the manufacturing conditions for barium titanate powder.

TABLE 2 Average Variation in capacitance capacitance (σ/ X) μF (%) Example [1] 1.08 1.7 Example [2] 1.01 2.0 Comparative 0.98 3.2 Example [1] Example [3] 1.11 1.8 Example [4] 1.12 1.5 Example [5] 1.14 2.3 Comparative 0.93 3.5 Example [2] Comparative 0.91 4.5 Example [3] Example [6] 1.03 1.5 Example [7] 1.04 2.1 Example [8] 1.03 2.5 Example [9] 1.02 1.9 Example [10] 1.04 2.1 Comparative 0.97 5.1 Example [4] Example [11] 0.95 2.8 Example [12] 0.95 2.7 Example [13] 0.98 2.7

In the present disclosure where conditions and/or structures are not specified, a skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. Also, in the present disclosure including the examples described above, any ranges applied in some embodiments may include or exclude the lower and/or upper endpoints, and any values of variables indicated may refer to precise values or approximate values and include equivalents, and may refer to average, median, representative, majority, etc. in some embodiments. Further, in this disclosure, an article “a” or “an” may refer to a species or a genus including multiple species, and “the invention” or “the present invention” may refer to at least one of the embodiments or aspects explicitly, necessarily, or inherently disclosed herein. In this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.

It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention. 

We/I claim:
 1. A multi-layer ceramic capacitor made by alternately layering a dielectric layer constituted by a sintered body of a ceramic powder, and an internal electrode layer, said ceramic powder containing barium titanate powder having a perovskite structure with a median size of 200 nm or smaller as measured by SEM observation, wherein the barium titanate powder is such that the percentage of barium titanate particles having twin defects in the barium titanate powder is 13% or more as measured by TEM observation and that its crystal lattice c/a is 1.0080 or more.
 2. A multi-layer ceramic capacitor according to claim 1, wherein the median size of the barium titanate powder is 80 to 200 nm.
 3. A multi-layer ceramic capacitor according to claim 1, wherein the percentage of barium titanate particles having twin defects in the barium titanate powder is 13 to 23%.
 4. A multi-layer ceramic capacitor according to claim 2, wherein the percentage of barium titanate particles having twin defects in the barium titanate powder is 13 to 23%.
 5. A multi-layer ceramic capacitor according to claim 1, wherein the crystal lattice c/a of the barium titanate powder is 1.0091 to 1.0105.
 6. A multi-layer ceramic capacitor according to claim 2, wherein the crystal lattice c/a of the barium titanate powder is 1.0091 to 1.0105.
 7. A multi-layer ceramic capacitor according to claim 3, wherein the crystal lattice c/a of the barium titanate powder is 1.0091 to 1.0105.
 8. A multi-layer ceramic capacitor according to claim 4, wherein the crystal lattice c/a of the barium titanate powder is 1.0091 to 1.0105. 